A group of Microsoft Products and technologies used for sharing and managing content, knowledge, and applications.
First, I recommend referring to the AI-generated answer, as it provides the recommended troubleshooting steps for the “UPLOAD BLOCKED” issue.
I’ve also included screenshots below for your reference.
1.Make sure the same account is used in OneDrive and PowerPoint desktop.
Please check the signed-in account in both OneDrive and PowerPoint and make sure they are using the same account.
2.Clear the stored OneDrive and Office credentials.
Open Credential Manager > Windows Credentials and remove the related OneDrive and MicrosoftOffice credentials. Then restart OneDrive and PowerPoint, sign in again using the same account, and try saving the file to OneDrive again.
3.Unlink and re-link OneDrive.
You can refer to the following article for more information and detailed steps: Unlink and re-link OneDrive | Microsoft Support
4.Install the latest Windows updates. After installing the available updates, restart the computer and test the file again.
For your reference: Install Windows Updates | Microsoft Support
I hope this helps.